Low Power Wide Area Networks (LPWANs) are increasingly seen as an attractive communication platform for city-scale Internet-of-Things (IoT) deployments. They can offer the ability to wirelessly connect energy-constrained devices to gateways over distances of many kilometers. LPWANs also have power and cost advantages over alternatives like cellular networks, particularly in deploy-once, low maintenance and low throughput sensing applications. While LPWANs are far from pervasive, the capabilities of networks like LoRaWAN, SigFox and Ingenu's RPMA have attracted investment and have spawned early deployments. These technologies operate on the unlicensed ISM spectrum, allowing businesses and consumers alike to deploy their own devices and gateways. Given that each LPWAN gateway promises a range of up to ten kilometers, major cities are likely to see a fast-paced expansion in LPWAN coverage.
Devices located in urban spaces deep inside buildings or in remote neighborhoods may experience severe drain in battery as their signals are highly attenuated even at the closest base station. Some of these devices, such as those in basements or tunnels, may not be in communication range of any gateway at all. Given that LPWANs are largely user-deployed and unplanned, many of these devices may remain battery deprived or simply out of network reach in perpetuity, even as thousands of gateways proliferate city-wide.
Private enterprises such as Semtech have developed LPWAN chipsets that use extremely narrow bands of unlicensed spectrum. In contrast, cellular standardization bodies have developed two standards for LPWAN communication for cellular base stations to communicate with low-power IoT devices over licensed spectrum: LTE-M and NB-IOT. Unlike LoRaWAN, these technologies may require devices to periodically wake up to synchronize with the network which may also reduce battery life.
Several recent measurement studies have been conducted to evaluate the performance and range of LPWAN networks and perform theoretical capacity analysis. Early pilot deployment efforts are also underway with SigFox deploying their hardware to connect security alarms to the cloud in Spain, smart blood refrigerators in the Democratic Republic of the Congo and smart city applications.
Multiple-antennas (MIMO) are known to improve SNR and reduce interference. In the WiFi context, past systems have used multi-user MIMO to improve performance on the uplink. In the cellular context, massive MIMO proposals have demonstrated scaling gains of towers with a large number of antennas. There has been much theoretical work on distributed MIMO overall in both the sensor networking context and wireless LANs and cellular networks. Practical distributed MIMO systems, primarily in the LAN-context, have demonstrated both multiplexing and diversity gains.
Multiple research efforts from the industry and academia have advocated the use of PHY layer processing at the cloud as opposed to the base stations. In the cellular context, CloudRAN aims to perform baseband processing at the cloud, allowing base stations to be simple and easy to deploy. One of the challenges however is the need for a reliable fiber optic backhaul to the cloud to collate data streams in a low latency manner, motivating the need for cost-effective high-performance backhauls.